Dating ductile deformation using U–Pb geochronology: examples from the Gilbert River Belt, Grenville Province, Labrador, Canada

1993 ◽  
Vol 30 (7) ◽  
pp. 1458-1469 ◽  
Author(s):  
D. J. Scott ◽  
N. Machado ◽  
S. Hanmer ◽  
C. Gariépy
Keyword(s):  
Isotopic Analysis ◽  
Shear Zones ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Grenville Province ◽  
Southern Limit ◽  
Zircon Age ◽  
Intense Deformation ◽  
Host Rocks

The Gilbert River Belt, in the Grenville Province in southeastern Labrador, is a distinctive, west–northwest-trending zone of locally intense deformation and voluminous granitoid plutonism, up to 30 km in width. In an attempt to directly quantify the timing of deformation in ductile shear zones within the belt, rocks interpreted as having been intruded synchronously with ongoing deformation were sampled for U–Pb isotopic analysis. Three of these samples are <2 m wide granitic veins that have sharp intrusive contacts that truncate ductile deformation fabrics, but are themselves deformed at metamorphic conditions similar to their host rocks and are therefore interpreted as having intruded after the initiation of deformation and fabric development, but prior to cessation of this deformation. The first vein is syntectonic with respect to amphibolite-facies deformation and yielded a zircon age of [Formula: see text]. The second vein intruded synchronously with the development of a zone of amphibolite-facies straight gneisses, which defines the southern limit of the Gilbert River belt at [Formula: see text]. The third vein is syntectonic with respect to greenschist-facies deformation and yielded a zircon age of [Formula: see text] and a monazite age of 1078 ± 2 Ma. A sample of the K-feldspar megacrystic granite that underlies much of the belt and is interpreted as having intruded during ongoing amphibolite-facies deformation yielded a zircon age of [Formula: see text]; a mildly deformed granitic vein that crosscuts the megacrystic granite at the same location contained zircon that indicate a [Formula: see text] crystallization age. Monazite from a granodioritic gneiss yielded a concordant age of 1077 ± 3 Ma, interpreted as the time of final cooling during gneiss formation. These results indicate that much of the amphibolite-facies deformation (1664 – 1644 Ma) in the Gilbert River Belt is correlative with the regionally extensive Labradorian orogenic event, whereas greenschist-facies deformation (1113 – 1062 Ma) and monazite growth (1078 Ma) are the result of renewed tectonomagmatic activity during Grenvillian orogenesis.

Pre-Grenvillian evolution and Grenvillian overprinting of the Parautochthonous Belt in Key Harbour, Ontario: U–Pb and field constraints

1994 ◽  
Vol 31 (3) ◽  
pp. 583-596 ◽  
Author(s):  
David Corrigan ◽  
Nicholas G. Culshaw ◽  
Jim K. Mortensen
Keyword(s):  
High Strain ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Grenville Orogeny ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
High Metamorphic Grade ◽  
Harbour Area ◽  
East West

The Parautochthonous Belt in the region of Key Harbour, Ontario, is composed of Early Proterozoic migmatitic para- and orthogneiss and Mid-Proterozoic granitoids, which were reworked during the Grenville orogeny. Grenvillian deformation is localized into anastomosing arrays of high-strain shear zones enclosing elongate bands and lozenges of rock subjected to lower and near-coaxial strain. Crosscutting relationships preserved in the low-strain domains document two pre-Grenvillian plutonic and tectonometamorphic events, which are bracketed in age by U–Pb zircon geochronology. A 1694 Ma leucogranite intrudes, and provides a minimum age for, high metamorphic grade gneisses formed during an earlier tectonometamorphic event (D1–M1). The leucogranite was intruded by mafic dykes, deformed, and metamorphosed at uppermost amphibolite facies during D2–M2, before the emplacement of Mid-Proterozoic granitoids at ca. 1450 Ma. Following the emplacement of gabbro dykes and pods at ca. 1238 Ma, the area was overprinted by granulite to uppermost amphibolite facies metamorphism (Grenvillian), for which monazites provide a minimum age of ca. 1035 Ma. Titanite U–Pb ages of 1003 – 1004 Ma record cooling through 600 °C. A regionally important swarm of east–west-trending posttectonic pegmatite dykes dated by U–Pb zircon at 990 Ma provides a minimum age for Grenvillian ductile deformation. The present data support the contention that the Parautochthonous Belt in the Key Harbour area consists in part of reworked midcontinental crust of Early to Mid-Proterozoic age.

Rapid fluid-driven transformation of lower continental crust associated with thrust-induced shear heating

2020 ◽  
Author(s):  
Bjørn Jamtveit ◽  
Kristina G. Dunkel ◽  
Arianne Petley-Ragan ◽  
Fernando Corfu ◽  
Dani W. Schmid
Keyword(s):  
Regional Metamorphism ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Source Rocks ◽  
Granitic Rocks ◽  
Time Interval ◽  
Fluid Infiltration ◽  
Facies Metamorphism ◽  
Shear Heating ◽  
Host Rocks

&lt;p&gt;Caledonian eclogite- and amphibolite-facies metamorphism of initially dry Proterozoic granulites in the Lind&amp;#229;s Nappe of the Bergen Arcs, Western Norway, is driven by fluid infiltration along faults and shear zones. The granulites are also cut by numerous dykes and pegmatites that are spatially associated with metamorphosed host rocks. U-Pb geochronology was performed to constrain the age of fluid infiltration and metamorphism. The ages obtained demonstrate that eclogite- and amphibolite-facies metamorphism were synchronous within the uncertainties of our results and occurred within a maximum time interval of 5 Myr, with a mean age of ca. 426 Ma. &amp;#160;Caledonian dykes and pegmatites are granitic rocks characterised by a high Na/K-ration, low REE-abundance and positive anomalies of Eu, Ba, Pb, and Sr. The most REE-poor compositions show HREE-enrichment. Melt compositions are consistent with wet melting of plagioclase- and garnet-bearing source rocks. The most likely fluid source is dehydration of Paleozoic metapelites, located immediately below the Lind&amp;#229;s part of the Jotun-Lind&amp;#229;s microcontinent, during eastward thrusting over the extended margin of Baltica. Melt compositions and thermal modelling suggest that short-lived fluid-driven metamorphism of the Lind&amp;#229;s Nappe granulites was related to shear heating at lithostatic pressures in the range 1.0-1.5 GPa. High-P (&amp;#8776;2 GPa) metamorphism within the Nappe was related to weakening-induced pressure perturbations, not to deep burial. Our results emphasize that both prograde and retrograde metamorphism may proceed rapidly during regional metamorphism and that their time-scales may be coupled through local production and consumption of fluids.&lt;/p&gt;

scholarly journals Structural setting and U–Pb zircon geochronology of the Glen Scaddle Metagabbro: evidence for polyphase Scandian ductile deformation in the Caledonides of northern Scotland

2008 ◽  
Vol 145 (3) ◽  
pp. 361-371 ◽  
Author(s):  
R. A. STRACHAN ◽  
J. A. EVANS
Keyword(s):  
Regional Metamorphism ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Zircon Geochronology ◽  
Zircon Age ◽  
Structural Setting ◽  
Facies Metamorphism

AbstractWithin the Scottish Caledonides, the Glen Scaddle Metagabbro was intruded into the Moine Supergroup of the Northern Highland Terrane after Grampian D2 folding and prior to regional D3 and D4 upright folding and amphibolite-facies metamorphism. A U–Pb zircon age of 426 ± 3 Ma obtained from the metagabbro is interpreted to date emplacement. D3–D4 folding is constrained to have occurred during the Scandian orogenic event. In contrast, polyphase folding and regional metamorphism of the Dalradian Supergroup southeast of the Great Glen Fault is entirely Grampian. These differences are consistent with published tectonic models that invoke a minimum of 700 km of post-Scandian sinistral displacements across the Great Glen Fault to juxtapose the Grampian and Northern Highland terranes.

Kanairiktok shear zone: the boundary between the Paleoproterozoic Makkovik Province and the Archean Nain Province, Labrador, Canada.

2000 ◽  
Vol 37 (9) ◽  
pp. 1245-1257 ◽  
Author(s):  
N Culshaw ◽  
T Brown ◽  
P H Reynolds ◽  
J WF Ketchum
Keyword(s):  
Shear Zone ◽  
Quartz Vein ◽  
Shear Zones ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Low Grade ◽  
Early Stages ◽  
Oblique Convergence ◽  
Andean Type ◽  
Early Activity

The polyphase Kanairiktok shear zone (KNSZ) separates gneissic rocks of the Archean Nain craton from their reworked equivalents in the Paleoproterozoic Kaipokok domain of the Makkovik Province. In its early stages, the KNSZ bounded the Kaipokok domain as it was thermally softened by 1895-1870 Ma Andean-type magmatism, accompanied by dextral oblique convergence and resultant penetrative deformation. The amphibolite-facies tectonite that developed in this stage was widely overprinted by greenschist-facies mylonite. Laserprobe and spectral 40Ar/39Ar ages of recrystallized and porphyroclastic muscovite, from the greenschist-facies mylonite and from muscovite in a syntectonic quartz vein, bracket the age of deformation between 1740 and 1710 Ma with the best estimate at 1715 Ma. These ages are similar to those of A-type granites within the Makkovik Province and amphibole cooling ages from the province interior. Together with the petrological similarity of the greenschist-facies mylonite to localized low-grade shear zones elsewhere in the Makkovik Province, they are suggestive of a widespread, lithosphere-scale event. The 40Ar/39Ar data do not provide good constraints on the early activity of the KNSZ. However, preservation of relationships between granitoid sheets correlated with the 1895-1870 Ma Island Harbour Bay plutonic suite and early fabrics imply that the granites were emplaced syntectonically in the KNSZ. Thus, the KNSZ was a major, long-lived structure in the Makkovik Province that decoupled events in the reactivated Nain craton from an inert cratonic region.

scholarly journals Structural and Compositional Evolution of Cr-Spinels and Hornblends, Palma Group, Rio Grande do Sul, Brasil

2000 ◽  
Vol 27 (1) ◽  
pp. 15 ◽  
Author(s):  
LÉO AFRANEO HARTMANN ◽  
MARCOS ANTONIO VASCONCELLOS ◽  
MARIA DE FÁTIMA BITTENCOURT ◽  
JOÃO CASTRO ◽  
JULIANA FABIÃO ◽  
...  
Keyword(s):  
Direct Contact ◽  
Rio Grande ◽  
Shear Zones ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Metamorphic Event ◽  
Rio Grande Do Sul ◽  
Compositional Evolution ◽  
Granite Intrusion

One amphibolite facies metamorphic event is registered in chromites and hornblendes from the Palma Group serpentinites and meta-andesites, Brazil's southernmost Rio Grande do Sui Slate. Metamorphism was apparently caused by syntectonic injection of voluminous Cambaí Group meta-granitoids and not by post-tectonic Jaguari Granite intrusion. Regional metamorphic hornblendes are in direct contact with magmatic pargasites, which indicates that it was the first metamorphic event in the area. Both hornblendes in Campestre Formation and Crspinels in Cerro da Cruz Formation are little zoned, an indication that only one metamorphic event was of regional extent. Recrystallization to chlorite + epidote greenschist facies parageneses is restricted to shear zones and volumetrically small.

The Patterson Lake corridor of Saskatchewan, Canada: defining crystalline rocks in a deep-seated structure that hosts a giant, high-grade Proterozoic unconformity uranium system

2020 ◽  
pp. geochem2020-007
Author(s):  
Colin D. Card
Keyword(s):  
Large Scale ◽  
Shear Zones ◽  
Crystalline Rocks ◽  
Ductile Deformation ◽  
Uranium Deposits ◽  
Content Type ◽  
Athabasca Basin ◽  
Rock Types ◽  
Host Rocks ◽  
Basin Region

The Patterson Lake corridor in the Athabasca Basin region of Saskatchewan, Canada hosts a large-scale uranium system with two major deposits already delineated. The corridor developed in crystalline rocks of the southwest Rae Province, which host all of the known uranium endowment. Orthogneisses along with voluminous pegmatites are the hosts of the uranium mineralization. These rocks, however, underwent significant open-system metasomatic – hydrothermal modification. Principal amongst these alterations is early and pervasive quartz flooding of the host rocks that resulted in the development of widespread secondary quartzites and associated rock types. These secondary quartzites and their altered host rocks suffered ductile deformation, typically focussed at silicification fronts. Late carbonatite dykes exploited the associated shear zones. Semi-brittle deformation zones nucleated near the previously developed ductile high-strain zones. Graphite and associated iron-sulphides precipitated in a semi-brittle structural regime. These graphitized zones provided the necessary structural architecture to focus the uranium system, which developed may be hundreds of millions of years younger developing at ∼1.425 Ga.Host rocks of the Patterson Lake corridor prove that metasedimentary rocks are not a requirement for development of giant Proterozoic unconformity uranium deposits. Crustal-scale fault zones with access to the mantle (i.e. carbonatites) should be considered a key parameter in the exploration model for Proterozoic unconformity uranium deposits. Given the similarity of the mineral assemblages in the crystalline basement rocks of the main exploration corridor to eastern Athabasca Basin region, it is likely that a similar, cryptic geological boundary focussed the giant uranium system in that region.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

scholarly journals Mid amphibolite facies metamorphism of harzburgites in the Neoproterozoic Cerro Mantiqueiras Ophiolite, southernmost Brazil

2003 ◽  
Vol 75 (1) ◽  
pp. 109-128 ◽  
Author(s):  
LÉO A. HARTMANN ◽  
FARID CHEMALE-JÚNIOR
Keyword(s):  
Mineral Assemblage ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Metamorphic Event ◽  
Mineral Equilibria ◽  
Facies Metamorphism ◽  
Geological Evolution ◽  
Mineral Compositions

Valuable information is retrieved from the integrated investigation of the field relationships, microstructure and mineral compositions of harzburgites from the Neoproterozoic Cerro Mantiqueiras Ophiolite. This important tectonic marker of the geological evolution of southernmost Brazilian Shield was thoroughly serpentinized during progressive metamorphism, because the oldest mineral assemblage is: olivine + orthopyroxene + tremolite + chlorite + chromite. This M1 was stabilized in mid amphibolite facies - 550-600ºC as calculated from mineral equilibria. No microstructural (e.g. ductile deformation of olivine or chromite) or compositional (e.g. mantle spinel) remnant of mantle history was identified. A metamorphic event M2 occurred in the low amphibolite facies along 100 m-wide shear zones, followed by intense serpentinization (M3) and narrow 1-3 m-wide shear zones (M4) containing asbestos.

Structural evolution of the Alaska Juneau lode gold deposit, southeastern Alaska

1992 ◽  
Vol 29 (5) ◽  
pp. 865-878 ◽  
Author(s):  
Lance D. Miller ◽  
Christopher C. Barton ◽  
Rick S. Fredericksen ◽  
Jason R. Bressler
Keyword(s):  
Gold Deposit ◽  
Structural Evolution ◽  
Structural Data ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Late Triassic ◽  
Lode Gold ◽  
Local Extension ◽  
Lode Gold Deposit ◽  
Host Rocks

The Alaska Juneau lode gold deposit is hosted by a series of polydeformed Permian to Late Triassic volcanic, pelitic, volcaniclastic, and mafic intrusive rocks. Rocks in the mine area have been sheared and metamorphosed to greenschist grade. Interpretation of rock fabrics indicates several generations of ductile and brittle deformation. Prior to mineralization, reverse shear occurred along northwest-striking and northeast-dipping ductile shear zones. Mineralization consists of Eocene auriferous quartz–carbonate veins, which cut the regional metamorphic fabrics. Mineralization was followed by reverse right-lateral shear along northwest-trending ductile–brittle shear zones. Two northwest-striking and steeply dipping vein sets host the bulk of the ore. Orientation of carbonate fibers within the quartz veins were used to determine the deformation regime that existed during mineralization. Plunge of the fibers indicate that down-to-the-northeast extension occurred synchronous with mineralization. Structural data support a model whereby the Alaska Juneau deposit formed after the peak of ductile deformation during a period of local extension. Localization of veins to areas of infolded phyllite and gabbro suggests that competency contrasts within host rocks enhanced vein emplacement. Veining may have been facilitated by a change from a contractional to a transpressive deformational regime which may have led to local extension and fluid migration to favorable deposition sites.

A seismic-based cross-section of the Grenville Orogen in southern Ontario and western Quebec

2000 ◽  
Vol 37 (2-3) ◽  
pp. 183-192 ◽  
Author(s):  
D J White ◽  
D A Forsyth ◽  
I Asudeh ◽  
S D Carr ◽  
H Wu ◽  
...  
Keyword(s):  
Cross Section ◽  
Seismic Refraction ◽  
Shear Zones ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Crustal Layer ◽  
Seismic Reflection Data ◽  
Velocity Models ◽  
Laurentian Margin ◽  
Structural Boundary

A schematic crustal cross-section is presented for the southwestern Grenville Province based on reprocessed Lithoprobe near-vertical incidence seismic reflection data and compiled seismic refraction - wide-angle velocity models interpreted with geological constraints. The schematic crustal architecture of the southwest Grenville Province from southeast to northwest comprises allochthonous crustal elements (Frontenac-Adirondack Belt and Composite Arc Belt) that were assembled prior to ca. 1160 Ma, and then deformed and transported northwest over reworked rocks of pre-Grenvillian Laurentia and the Laurentian margin primarily between 1120 and 980 Ma. Reworked pre-Grenvillian Laurentia and Laurentian margin rocks are interpreted to extend at least 350 km southeast of the Grenville Front beneath all of the Composite Arc Belt. Three major structural boundary zones (the Grenville Front and adjacent Grenville Front Tectonic Zone, the Central Metasedimentary Belt boundary thrust zone, and the Elzevir-Frontenac boundary zone) have been identified across the region of the cross-section based on their prominent geophysical signatures comprising broad zones of southeast-dipping reflections and shallowing of mid-crustal velocity contours by 12-15 km. The structural boundary zones accommodated southeast over northwest crustal stacking at successively earlier times during orogeny (ca. 1010-980 Ma, 1080-1060 Ma, and 1170-1160 Ma, respectively). These shear zones root within an interpreted gently southeast-dipping regional décollement at a depth of 25-30 km corresponding to the top of a high-velocity lower crustal layer.

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